In various applications that require transparency and coloring, thermoplastic elastic rubber compositions in which an inorganic filler has been blended in a thermoplastic elastic body have conventionally been reported. For example, there are rubber compositions comprising a thermoplastic elastic body and silica, rubber compositions comprising a thermoplastic elastic body and titanium oxide, and the like.
Also, usually in the blending of vulcanized rubbers, when a closed-type mixer for example a Banbury mixer or an internal mixer is used to add and knead an inorganic filler and the like, temperature rises as soon as rubber mastication is started, and during the process of rising temperature an inorganic filler etc. are added, and it reaches a temperature higher than 60° C. before the passage of 30 seconds at the latest after the start of kneading.
When an open roll etc. is used, kneading has been performed at a high rubber temperature exceeding 60° C. in order to enhance rubber plasticity and facilitate kneading.
JP-A-62-137002 relates to shoe soles having an excellent coloring and abrasion resistance obtained by specifying silica and a silane coupling agent and mixing rubber with a thermoplastic resin, and describes that coloring may be effected without using carbon black.
JP-A-2000-236905 discloses a light-weight abrasion resistant soling material comprising a high cis-polybutadiene, a styrene resin and silica.
JP-A-2001-161404 describes shoe soles in which rubber and silica have been and the gravity thereof has been specified.
Rubber compositions using a thermoplastic elastic body indeed have transparency and coloring to a certain degree, but they have problems of poor c-set and poor abrasion resistance, and poor oil resistance. In rubber compositions for which such transparency and coloring are required, attaining balances between transparency and physical properties such as c-set and abrasion resistance while maintaining sufficient transparency have not been sufficient. On the other hand, in rubber compositions in which oil resistance has been improved by vulcanization of styrene butadiene rubber, there are problems that when the amount of inorganic fillers is reduced in order to enhance transparency and coloring properties, the physical properties of the vulcanized rubber compositions such as c-set and abrasion resistance become decreased, and conversely when the amount of inorganic fillers is increased, these physical properties may be enhanced to a certain degree but transparency and coloring properties become decreased.
It is an object of the present invention to provide transparent rubber compositions having an excellent transparency and coloring properties, and rubber properties such as c-set and abrasion resistance, methods of producing them, and footwear having excellent designing and functional properties using said transparent rubber compositions.